nano 2007-10-23 11:21
Magnetic bubbles appear in nanodots
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【纳米科技世界快讯】Scientists have observed mathematical objects called magnetic bubbles in nanodots with strong perpendicular anisotropy. They have also seen triple-domain states consisting of concentric rings with alternating magnetisation in the same material. As well as being of interest for fundamental studies in physics, the magnetic structures might also be used in information data-storage applications.8cDc$}7x#\p2y
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"In the nanoscale magnetic particles we studied (made of iron-platinum), the magnetic dipoles of the atoms are organised in configurations, or magnetic distributions, some of which can be particularly interesting," team member Christoforos Moutafis of Cambridge University, UK, told nanotechweb.org. "The axially symmetric magnetic states we have identified are manifestations of non-trivial mathematical objects."
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[i]An image (vector plot) that represents the magnetization on the top surface of a nanodot in the monobubble state. Credit: C Moutafis.[/i]
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The team, which also includes researchers from Japan and Germany, observed the magnetic structures using magnetic force microscopy, by imaging arrays of dots with various diameters. In small dots they identified robust circular magnetic bubbles that were confined in the centre of the dots. "These are cylindrical domains of magnetization anti-parallel to its surroundings and perpendicular to the nanodot," explained Moutafis. "We have called this bi-domain state the 'monobubble' state."s)Fr C*{ X
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In larger dots, random labyrinth-like magnetic patterns were seen with the monobubbles only appearing at certain dot diameters and thicknesses. According to the researchers, the bubbles resemble the magnetic vortices commonly seen in low anisotropy magnetic particles with the outer domain wall running around in a circle. Tri-domain – or three-ring – states, which are concentric rings with alternating magnetisation, were also observed. These have been dubbed higher-order bubble states by the team.
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"Magnetic nanodots are 'labs' for studying a hierarchy of mathematical objects," said Moutafis. "The FePt alloy also has some extraordinary magnetic properties, such as strong magnetic anisotropy, which makes it a candidate for future technological applications like data storage."A*sp*k6z0LA b
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[i]Christoforos Moutafis in the lab alongside a poster that describes his work. (Credit: C Moutafis)[/i]
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Moutafis goes on to say that the magnetic states observed respond in a distinct way when probed externally, for example with an applied field or currents. "This is significant both for fundamental research and potential applications. Our work shows a way to explore the dynamics of such magnetic configurations at the nanoscale.".aaH8b nx&D0n|
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A detailed knowledge of these states and how they evolve would allow them to be manipulated in a controlled way. For example, this would mean that a single nanodot could be used to code several bits of information simply by changing its magnetic state. "This may find applications, for example, in magnetic tags that could be used for biological assays, or in general devices where there is a need for coding information," explained Moutafis.1P$Z `p/gFo%@#p
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The researchers have now begun computational modelling of these phenomena and also plan to do more imaging experiments. "It is fascinating to find (based on preliminary results) that transient phenomena at extremely small timescales seem to mediate the switching between the different magnetic configurations and dominate their dynamics," said Moutafis. "Apart from scientific interest, the potential of ultra-fast switching is very important for technology since this means short operation times, a prerequisite in modern devices."M2]4k[zxv
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The researchers reported their work in [url=http://link.aps.org/abstract/PRB/v76/e104426][color=#0000ff][i]Phys. Rev. B[/i] [b]76[/b] 104426[/color][/url].#O-?sl-S+?#Y-U3q
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Source：nanotechweb.org